Method for Evaluating Properties of Melt-Blown Plastic Resin

ABSTRACT

A method for evaluating physical properties of a melt-blown plastic resin, and, more specifically, a novel method for evaluating physical properties are provided. When a particular plastic resin is processed by a melt-blown process, a stretching diameter value after the process of the plastic resin can be accurately derived from a physical property value measured using a specimen of the resin.

TECHNICAL FIELD Cross-Reference to Related Application(s)

This application claims priority to or the benefit of Korean PatentApplication No. 10-2017-0118860 filed with the Korean IntellectualProperty Office on Sep. 15, 2017, the disclosure of which isincorporated herein by reference in its entirety.

The present invention relates to a method for evaluating physicalproperties of a melt-blown plastic resin. More specifically, the presentinvention relates to a method for evaluating physical properties inwhich, when a particular plastic resin is processed by a melt-blownprocess, a stretching diameter value after the melt-blown process can beaccurately derived from a physical property value measured using aspecimen of the resin.

BACKGROUND ART

Nonwoven fabric or nonwoven web is a three-dimensional fiber aggregatein which fine fibers having a diameter of about 10 μm are randomlyentangled to have a structure like a spider web.

Since the nonwoven fabric or the nonwoven web is formed by bonding finefibers to each other, the nonwoven fabric or the nonwoven web is veryexcellent in texture, touch, or the like, and has good processabilityand excellent strength, ductility, and abrasion resistance.

Such nonwoven fabric is used for various purposes in various technicalfields, such as bandage materials, oil absorbing materials, buildingmaterials for sound absorption, disposable diapers, feminine hygieneproducts or the like. In recent years, it is widely used also in thelatest technology fields, such as dustproof clothing, a dustproof mask,a wiping cloth, a microfiltration filter, and a battery separator.

There are known several types of processes for producing a nonwovenfabric or a nonwoven web, but among them, a melt-blown process is mostfrequently used. The melt-blown process is a process in which thethermoplastic resin capable of forming a fiber yarn is discharged in amolten form through an orifice die to which a plurality of orificeshaving hundreds to thousands of cavities are connected, ahigh-temperature gas is injected from high-speed gas nozzles disposed onboth sides of the die, fiber yarns are stretched into ultrafine yarns,and the ultrafine fiber yarns are laminated on the collection drum.

Such melt blown nonwoven fabrics can be used in various applications asdescribed above due to the structural features in which the ultrafinefiber aggregates are formed into a bulky structure.

In a normal melt blown process, as plastic resin is discharged from anorifice die and stretched by the high-temperature gas, the diameter ofthe fiber yarn is determined, which is greatly affected by theproperties of the plastic resin itself as well as the dischargepressure, gas temperature, and gas injection speed.

In particular, since the diameter of the fiber yarn varies depending onthe use of the nonwoven fabric, it is necessary to adjust the diameterof the fiber yarn according to the conditions in the melt-blown process.Conventionally, in order to confirm the diameter of the fiber yarn,there was only a method of proceeding the melt-blown process to directlyconfirm the diameter. A method of predicting the diameter prior toproceeding the process was not known.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

It is an object of the present invention to provide a method forevaluating physical properties of a melt-blown plastic resin in which,when a particular plastic resin is processed by a melt-blown process, astretching diameter value after the melt-blown process can be accuratelyderived from a physical property value measured using a specimen of theresin.

Technical Solution

One aspect of the present invention provides a method for evaluatingphysical properties of a melt-blown plastic resin including the stepsof:

measuring a molecular weight distribution for a plastic resin specimen;

deriving a peak molecular weight value from the molecular weightdistribution;

deriving a molecular weight distribution value (Mw/Mn) from themolecular weight distribution; and

predicting a stretching diameter in a melt-blown process using the peakmolecular weight value and the molecular weight distribution value.

Advantageous Effects

According to the present invention, even if a plastic resin is notactually put into the melt-blown process, the diameter of the fiber yarnproduced in the melt-blown process can be accurately derived only by thephysical properties measured by a specimen, which is thus economical interms of time and money.

Detailed Description of the Embodiments

The method for evaluating physical properties according to the presentinvention includes the steps of:

measuring a molecular weight distribution for a plastic resin specimen:

deriving a peak molecular weight value from the molecular weightdistribution;

deriving a molecular weight distribution value (Mw/Mn) from themolecular weight distribution; and

predicting a stretching diameter in a melt-blown process using the peakmolecular weight value and the molecular weight distribution value.

The terminology used herein is for the purpose of describing particularexemplary embodiments and is not intended to be necessarily limiting ofthe present invention. As used herein, the singular forms “a,” “an” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. The terms “comprises,” “includes”or “have” when used in this specification, specify the presence ofstated features, integers, steps, components, or combinations thereof,but do not preclude the presence or addition of one or more otherfeatures, integers, steps, components or combinations thereof.

Since the present invention may be modified in various forms, and mayhave various embodiments, the following exemplary embodiments areillustrated and described in detail. However, this is not intended tolimit the present invention to specific embodiments, and the presentinvention should be construed to encompass various changes, equivalents,and substitutions within the technical scope and spirit of theinvention.

Throughout this specification, the plastic resin is a concept includinga thermoplastic polymer plastic, and means a polymer plastic resin thatcan be processed into a fiber yarn form by a melt-blown process.

Hereinafter, embodiments of the present invention will be described indetail.

The method for evaluating physical properties of a melt-blown plasticresin according to one aspect of the present invention includes thesteps of:

measuring a molecular weight distribution for a plastic resin specimen;

deriving a peak molecular weight value from the molecular weightdistribution;

deriving a molecular weight distribution value (Mw/Mn) from themolecular weight distribution; and

predicting a stretching diameter in a melt-blown process using the peakmolecular weight value and the molecular weight distribution value.

The present inventors have made a hypothesis that in the melt-blownmolding process of a plastic resin, the stretching diameter of the fiberyarn discharged and processed by the cavity of the orifice is related tothe molecular weight characteristics of the plastic resin, and then havefound that the stretching diameter of the actual fiber yarn can beaccurately derived through specific factors that can be measured fromplastic resin specimens, thereby completing the present invention.

Specifically, for the plastic resin specimen, the molecular weightdistribution value is measured using a measuring instrument such as GPC,and a peak molecular weight value and a molecular weight distributionvalue are derived from the molecular weight distribution, and then fromthese two values as relevant factors, the stretching diameter value ofthe fiber yarn can be accurately derived in the melt-blown process.

The peak molecular weight value means a molecular weight valuecorresponding to the largest peak when the molecular weight distributionof the plastic resin specimen was measured by GPC/SEC, that is, amolecular weight value of the molecule occupying the highest fraction inthe plastic resin including molecules having various molecular weightvalues.

And, since the stretching diameter value of the fiber yarn formed by themelt-blown process is a value that can vary depending on the conditionsof the process, the melt-blown process may be performed under thetemperature condition of about 150° C. to about 250° C., preferably at atemperature of about 170° C. or about 230° C. However, the presentinvention is not necessarily limited to the above-mentioned processconditions, and this may vary depending on the melting characteristicsof the plastic resin to be processed.

In addition, the stretching diameter value of the fiber yarn formed bythe melt-blown process is a value that may vary depending on the stretchratio in the process. In the melt-blown process, the longitudinalstretch ratio may be about 100 to about 10,000 times, preferably about100 to about 1,500 times, or about 200 to about 1.200 times.

In this case, the stretching speed may be about 1,000 to about 100,000times/s, preferably about 1000 to about 15,000 times/s, or about 200 toabout 1,200 times/s.

However, the present invention is not necessarily limited to theabove-mentioned process conditions, and the stretching conditions asabove may also vary depending on the melting characteristics of theplastic resin to be processed.

Further, the step of predicting the stretching diameter using the peakmolecular weight value and the molecular weight distribution value mayinclude a step of deriving a polymer characteristic factor usingMathematical Formula 1 below, and it may include a step of predicting astretching diameter from this polymer characteristic factor usingMathematical Formula 2 below.

Polymer Characteristic Factor=a(MWD)^(b)*(Mp)^(c)  [Mathematical Formula1]

in Mathematical Formula 1.

MWD is a molecular weight distribution value (Mw/Mn),

Mp is a peak molecular weight value,

a is 0.01 to 0.02.

b is 0.8 to 1.0, and

c is 0.20 to 0.22.

Predicted Stretching Diameter=d*(polymer characteristicfactor)−e  [Mathematical Formula 2]

in Mathematical Formula 2,

d is 1.01 to 1.02, and

e is 0.005 to 0.007.

In other words, it is possible to predict the stretching diameter of afiber yarn formed in a melt-blown process by substituting the molecularweight distribution value and the peak molecular weight value, which areconfirmed by measuring the molecular weight distribution, intoMathematical Formula 1 above, introducing the value of each coefficientaccording to the molecular weight characteristics and meltingcharacteristics of a target plastic resin, then deriving the polymercharacteristic factor of the plastic resin according to a simplecalculation formula, and then again substituting this factor intoMathematical Formula 2.

More specifically, the value of each coefficient of MathematicalFormulae 1 and 2 may be determined by the steps of measuring thestretching diameter values of a fiber yarn in the actual melt-flownprocess for some plastic specimens, measuring the above-mentioned MWDvalue and Mp value, and then substituting the measured values into thefunctions represented by Mathematical Formulae 1 and 2 to derive thevalue of each coefficient, and this can be used as a reference.

In particular, in the case of Mathematical Formula 1, if log is taken onboth sides of the function, it will have the form of simultaneous linearequations with three variables. Thus, even if measured and calculated bytaking at least three plastic resin specimens for predicting thestretching diameter of a fiber yarn, accurate coefficient values can bederived. By using these values, the value of each coefficient forvarious plastic resins can be used as a reference.

In the case of polypropylene resin, in Mathematical Formula 1, a mayhave a value of about 0.01 to about 0.02, preferably about 0.012 toabout 0.015, b may have a value of about 0.8 to about 1.0, preferablyabout 0.85 to about 0.90, and c may have a value of about 0.2 to about0.22, preferably about 0.205 to about 0.210.

Further, in Mathematical Formula 2, d may have a value of about 1.01 toabout 1.02, preferably about 1.015 to about 1.017, e may have a value ofabout 0.005 to about 0.007, preferably about 0.006 to 0.0061.

However, the present invention is not necessarily limited to the rangeof the respective coefficients a to e described above, and respectivecoefficients may be determined differently according to the molecularweight and melting characteristics of the plastic resin to be measured.

And, according to one embodiment of the present invention, when thepredicted stretching diameter is about 0.35 mm or less, more preferably,when it is about 0.2 to about 0.35 mm, it can be determined to besuitable.

Specifically, the melt-blown process under the above-describedconditions may be regarded as a process of forming a fiber yarn fornonwoven fabric production. If the stretching diameter of the fiber yarnin the actual process is too large, the texture of the nonwoven fabricproduced is degraded, sound absorption or sound insulation propertiesmay be degraded. If the stretching diameter is too small, it may cause aproblem that the mechanical strength of the nonwoven fabric is lowered.

The method for evaluating physical properties according to the presentinvention as described above is applicable to various plastic polymerresins which are produced in the form of fiber yarn by a melt-blownprocess.

As an example, the method may be applied to a plastic resin in which theabove-mentioned peak molecular weight value is about 10.000 to about150.000 g/mol, preferably about 30,000 to about 120.000 g/mol.

According to another embodiment of the present invention, the method maybe applied to a plastic resin in which the above-described molecularweight distribution value, that is, the ratio (Mw/Mn) of the weightaverage molecular weight value to the number average molecular weightvalue is about 4 or less, preferably about 1 to 4, more preferably about2 to about 3.5.

Further, the method may be applied to a plastic resin in which thenumber average molecular weight value is about 10,000 to about 50,000g/mol, preferably about 20,000 to about 45.000 g/mol. The weight averagemolecular weight value of such plastic resin may be preferably about10,000 to about 200,000 g/mol, preferably about 50,000 to about 140,000g/mol.

And specifically, polystyrene-based resin, polyolefin-based resin,polyvinyl chloride-based resin, poly (meth)acrylic-based resin,polyamide-based resin. ABS-based resin, urethane epoxy-based resin,urethane acrylic-based resin, amino resin, phenol resin, andpolyester-based resin are subjected to a melt-blown molding process toform a fiber yarn, and such fiber yarn can be applied for variousplastic resins that are processed into products, but when it is appliedfor a thermoplastic resin, more accurate evaluation results can bepresented. Among them, it may be preferably applied to apolyolefin-based resin such as polyethylene and polypropylene resin,among which polypropylene-based resin is most preferred.

Hereinafter, the functions and effects of the present invention will bedescribed in more detail with reference to examples. However, theseexamples are given for illustrative purposes only and are not intendedto limit the scope of the present invention.

Example

Preparation of Plastic Resin Specimen

The polypropylene resin having physical property values shown in Table 1below was dried in a vacuum oven at 40° C. overnight to prepare in theform of pellets using a twin screw extruder (BA-19, manufacturerBAUTECH).

The resin in the form of pellets obtained by compression was again driedin a vacuum oven at 40° C. overnight, and then a specimen was preparedin a form suitable for the measurement conditions of each physicalproperty using a specimen manufacturing machine (Xplore 5.cc microinjection molding machine).

1) Measurement of Molecular Weight Characteristics

Molecular weight characteristics of the prepared specimens were measuredvia GPC/SEC. The number average molecular weight, the weight averagemolecular weight, the molecular weight distribution value, and the peakmolecular weight value were simultaneously measured.

The peak molecular weight value and the molecular weight distributionvalue were substituted into the following Mathematical Formulas topredict the stretching diameter value of the fiber yarn after themelt-blown process.

Polymer Characteristic Factor=a(MWD)^(b)*(Mp)^(c)  [Mathematical Formula1]

Predicted Stretching Diameter=d*(Polymer CharacteristicFactor)−e  [Mathematical Formula 2]

In Mathematical Formula, each coefficient is a value corresponding topolypropylene, and a=0.01463, b=0.8854, c=0.2066, d=1.01687, ande=0.00607, respectively.

2) Measurement of Stretching Diameter of Fiber Yarn

For accurate stretching diameter measurement, a DHR (Discovery HybridRheometer) from TA Instruments used for measurement of flow propertiesof the fluid was used.

The prepared polypropylene pellet was melted and loaded between theupper and lower plates of the DHR. (conditions of temperature: 170° C.,initial diameter of PP loaded between upper and lower plates: 8 mm,initial thickness: 1.5 mm).

The molten PP, which was loaded between the upper and lower plates, wasstretched while the upper plate of the DHR was raised to a stretchingspeed of 10 mm/s, which was taken with an ultrafast camera (IDT'sCrashCam 1520), and the diameter of the stretched PP was measuredthrough image analysis (analysis tool: imageJ).

The molecular weight-related measured values are summarized in Table 1below. Polymer characteristic factors, predicted diameter values, andmeasured diameter values derived therefrom are summarized in Table 2below.

TABLE 1 Number Weight average average Molecular Peak molecular molecularweight molecular weight weight distribution weight (g/mol) (g/mol)(Mw/Mn) (g/mol) Example 1 22055 52625 2.39 40,371 Example 2 40385 932642.31 72,898 Example 3 35326 90003 2.55 83,935 Example 4 26605 57806 2.1755,674 Example 5 22156 49442 2.23 45,953 Example 6 23764 54845 2.2056,638 Example 7 25328 57571 2.27 58,453 Example 8 39255 137899 3.51104,164 Example 9 42560 128591 3.02 96,022 Example 10 42326 134202 3.17105,590 Example 11 44496 131242 2.95 102,759

TABLE 2 Polymer Predicted Measured Stretch character- diameter diameterratio istic value value (times) factor (mm) (mm) Example 1 1093 0.2830.282 0.242 Example 2 756 0.310 0.309 0.291 Example 3 425 0.349 0.3490.388 Example 4 954 0.278 0.276 0.259 Example 5 1093 0.273 0.272 0.242Example 6 761 0.282 0.281 0.290 Example 7 653 0.292 0.291 0.313 Example8 284 0.484 0.486 0.475 Example 9 359 0.417 0.417 0.422 Example 10 3370.443 0.445 0.436 Example 11 443 0.414 0.415 0.380

Referring to Table 1 above, it can be clearly seen that the tensilediameter of the fiber yarn predicted according to one example of thepresent invention has a value very similar to that of the fiber yarnmeasured in the actual process.

In particular, when the actual diameter value and the predicted diametervalue are compared and verified, the Pearson correlation coefficientvalue appears to reach about 0.92, confirming that it has a very highcorrelation. Although respective stretch ratios are different whenstretched at the same speed, it can be confirmed that the correlationbetween the actual value and the predicted value is very high. This canbe seen as clearly explaining that the actual tensile diameter value ofthe plastic resin fiber yarn is directly related to the above-describedmolecular weight distribution value and peak molecular weight value.

When the actual tensile diameter value of the plastic resin fiber yarnis not directly related to the above-mentioned molecular weightdistribution value or peak molecular weight value, irrespective of eachcoefficient value in Mathematical Formulae 1 and 2 above, the predictedtensile diameter value cannot converge to the actual tensile diametervalue.

However, the actual tensile diameter value of the plastic resin fiberyarn is clearly verified as having a first order correlation with thevalue predicted by Mathematical Formulae 1 and 2. This can be said to bethe result clearly supporting that as shown in the present invention, inthe melt-blown process of the plastic resin, the tensile diameter valueof the fiber yarn has a direct correlation with the molecular weightcharacteristic of each plastic resin, regardless of each coefficientvalue used in Mathematical Formulae 1 and 2.

1. A method for evaluating physical properties of a melt-blown plasticresin comprising: measuring a molecular weight distribution for aplastic resin specimen; deriving a peak molecular weight value from themolecular weight distribution; deriving a molecular weight distributionvalue (Mw/Mn) from the molecular weight distribution; and predicting astretching diameter of the plastic resin specimen manufactured from amelt-blown process using the peak molecular weight value and themolecular weight distribution value.
 2. The method according to claim 1,wherein when the molecular weight distribution of the plastic resinspecimens is measured by GPC/SEC, the peak molecular weight value is amolecular weight value corresponding to a largest peak.
 3. The methodaccording to claim 1, wherein the melt-blown process is performed underthe temperature condition of 150° C. to 250° C.
 4. The method accordingto claim 1, wherein the melt-blown process is performed at alongitudinal stretch ratio of 100 times to 10,000 times.
 5. The methodaccording to claim 1, wherein predicting the stretching diametercomprises: deriving a polymer characteristic factor using MathematicalFormula 1 below.Polymer Characteristic Factor=a(MWD)^(b)*(Mp)^(c)  [Mathematical Formula1] in Mathematical Formula 1, MWD is the molecular weight distributionvalue (Mw/Mn), Mp is the peak molecular weight value, a is 0.01 to 0.02,b is 0.8 to 1.0, and c is 0.20 to 0.22.
 6. The method according to claim5, wherein predicting the stretching diameter comprises; predicting astretching diameter from the polymer characteristic factor usingMathematical Formula 2 below.Predicted Stretching Diameter=d*(Polymer CharacteristicFactor)−e  [Mathematical Formula 2] in Mathematical Formula 2, d is 1.01to 1.02, and e is 0.005 to 0.007.
 7. The method according to claim 1,wherein the peak molecular weight value is 10.000 g/mol to 150,000g/mol.
 8. The method according to claim 1, wherein the molecular weightdistribution value is 4 or less.
 9. The method according to claim 1,wherein the plastic resin has a number average molecular weight value(Mn) of 10,000 g/mol to 50,000 g/mol.
 10. The method according to claim1, wherein the plastic resin has a weight average molecular weight value(Mw) of 10,000 g/mol to 200,000 g/mol.
 11. The method according to claim1, wherein the plastic resin is a polypropylene resin.